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Published byElisha Vidal Modified over 9 years ago
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NCHRP Projects 9-25 & 9-31: Findings Related to Surface Cracking FHWA Mixture ETG Washington, DC February 2003 Advanced Asphalt Technologies, LLC “Engineering Services for the Asphalt Industry”
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Fatigue Testing and Analysis Continuum damage approach Normalization to reduce or eliminate effect of mixture stiffness Produces single continuum damage fatigue constant “C**2” characteristic of intrinsic fatigue resistance Independent of stress- vs. strain-control
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Effective Binder Content
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WesTrack Cracking Vs. Vbe
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Mixture Stiffness Increased mixture stiffness decreases strains Decreased strains increases fatigue life HOWEVER…
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Binder Viscosity & Healing Healing more rapid with low viscosity binders Generally, fatigue resistance will decrease with increased high- temperature binder grade
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Healing and Binder Viscosity (after Little et al., 1999)
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Age Hardening |G*| aged / |G*| unaged = 1.76 0.0037(% LS) + 0.028 (VTM) 0.068 (Agg. S.A.) R 2 = 74 %
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Age Hardening: Aggregate Type and Permeability Limestone fines appears to significantly retard age hardening Age-hardening also decreases with decreasing permeability –Increasing aggregate surface area –Decreasing air voids
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Summary: Factors Affecting Fatigue Cracking Effective binder content Structural stiffness Mixture stiffness Binder viscosity & healing Mixture age hardening
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Ways to Increase Fatigue Life Increase binder content Decrease binder viscosity Increase pavement thickness Use limestone/hydrated lime fines and/or filler
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Controlling Rut Resistance Rut resistance a function of –Binder grade –N-design –VMA relative to aggregate fineness To maintain rut resistance with increased binder, increase proportion of fines/mineral filler
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Mix Resistivity
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Recommendations Use 9.5 and 12.5-mm mixtures for wearing courses Increase binder 0.5 % by weight Maintain filler/binder ratio Avoid unnecessary grade bumping Use limestone/hydrated lime fines and mineral filler
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What Can 0.5 % Change in Binder Content Do?
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